The present invention relates to an arrangement and method of control thereof of a reciprocating piston internal combustion engine utilized in a vehicle with vacuum powered components. In particular, the present invention relates to such a vehicle with a reciprocating piston variable displacement engine having selective cylinder deactivation.
Four-stroke, multiple-cylinder, reciprocating piston internal combustion engines used in automobiles are capable of being operated over great speed and load ranges. Those skilled in the art have recognized for years that lower specific fuel consumption is usually achieved when an engine is operated at a relatively high load. This is particularly true for spark ignition engines because throttling losses are minimized when the engine is operated at or near wide open throttle at full load conditions. Unfortunately, engines are frequently required to operate at less than maximum load. When an engine operates at partial load, fuel economy suffers because of the pumping loss. Therefore, it is desirable to avoid partial load operation of the engine.
Engines have been designed that avoid partial load operation by deactivating selected cylinder combustion chambers to allow the remaining active chambers to be operated at higher loads. Such engines are often referred to as variable displacement engines. Deactivation of the cylinders is typically achieved by a lost motion rocker arm assembly which can be selectively disabled, therefore allowing the valves associated with the given cylinder to remain in a deactivated closed position regardless of the position of an associated camshaft. At the time of a valve deactivation, the fuel injectors associated with the deactivated cylinders are also deactivated. Deactivation of cylinders may also be achieved by utilizing a variable cam timing unit to change the phase of operation of the exhaust or the intake valves.
As used in this application, the term xe2x80x9cdeactivated cylinderxe2x80x9d may refer to a cylinder that is deactivated by a valve that is deactivated in an opened or closed position. xe2x80x9cDeactivated cylinderxe2x80x9d may also refer to a valve that is deactivated by its change of phase in relationship to the angular position of an engine crankshaft or to a cylinder deactivated by other means.
A further explanation of other schemes used in variable displacement engines with valve deactivation can be gained by a review of Russ, et al., U.S. Pat. No. 6,237,559, Stockhausen, et al., U.S. Pat. No. 5,642,703 and Stockhausen U.S. Pat. No. 5,467,748 commonly assigned.
On variable displacement engines, such as those which deactivate a bank of cylinders that have dual independent intake systems and dual independent throttle valves, it is often necessary to implement a vacuum control system. (See U.S. patent application Ser. No. 09/682,695 filed Oct. 5, 2001.) At light loads, the engine is typically operating with half its cylinders deactivated, to reduce engine throttle. Since the engine has less throttle on a particular bank of cylinders, the manifold pressure exposed to that bank will be higher. The disadvantage of operating in a deactivated mode for long periods of time is that systems that depend upon a vacuum force for power may not operate properly. Examples of such systems are the brake system master cylinder booster, vacuum actuated engine gas recirculation valve systems and heating, vacuum and air conditioning vent controls.
Prior to the present invention, the lack of vacuum to power systems was often addressed by using a hydraulic boost pump which worked off the power steering pump, or by having an electric powered vacuum pump. The use of a hydraulic or electric pump is typically undesirable since the hydraulic boost pump adds cost and weight to the vehicle and may be a source of parasitic power losses when not being utilized. The electric vacuum boost pump also adds an additional component, weight and cost to the vehicle.
It is desirable to provide an arrangement and method of operation thereof of a vehicle with a variable displacement engine wherein the vacuum system can be managed to ensure proper vacuum power ability without the addition of a hydraulic or electric boost pump.
In a preferred embodiment, the present invention provides an arrangement of a vehicle with a variable displacement engine having a first group of cylinders which are normally always activated and a second selectively valve deactivated group of cylinders. A sensor is provided in the vacuum system to alert the engine controller whenever the vacuum level within the vacuum system is below a predetermined desired value. The vacuum level can also be inferred by engine operational parameters or by vehicle brake system operational history. Upon recognition of a low vacuum level, the engine controller will modify the engine operation to raise the vacuum level.
The controller can sequentially or non-sequentially select among three main engine operational options to raise the vacuum level including: (1) the controller can advance the variable time caming on the first group of cylinders; and (2) the controller can cause one or more of the second group of cylinders to be valve activated to pump air from the engine manifold. Typically, such an engine will have independent control of dual throttles and the controller will additionally close the throttle that is operatively connected with the second group of cylinders. If options (1) and (2) are insufficient, the controller can additionally cause all or part of the fuel injectors of the second group of cylinders to resume operation and for the ignition system to fire the cylinder.
The present invention is advantageous in that it maintains proper vacuum level in a vacuum system without the requirement of additional hydraulic or electric pumps and the cost and weight associated with such systems.
It is an advantage of the present invention to provide an arrangement of an automotive vehicle having a variable displacement engine wherein the vacuum level of the vacuum system is maintained.
It is a further advantage of the present invention to do the above noted task without the additional cost and weight associated with a vacuum pump powered by the power steering pump of the vehicle or a separate vacuum pump which is electrically powered.
Other advantages and features of the present invention will be further realized from the review of the invention as it is disclosed in the detailed description and accompanying drawings.